Citing the Heritage Foundation's 2014 Index of Culture and Opportunity, the Daily Signal reported 40.9 percent of unmarried female-headed families with children were poor in 2012 – and the Census report noted similar findings.

"Research shows that women with a nonmarital first birth are both less likely to ever marry and less likely to remain married if they do marry," it said.

Childbearing outside of marriage is also linked to higher risks for poverty, lower educational attainment and family instability.

"It's important to track these changes in fertility because recent research suggests that childbearing is related to women's rates of employment, their educational attainment and their economic well-being," study researcher Lindsay Monte told The Washington Times.

But the Census report, "Fertility of Women in the United States: 2012" released earlier this month, noted the sinking percentage of married first-time moms doesn't mean the women were necessarily single or raising the baby with an absent father.

About 25 percent of all first-time mothers are living with their partners, up from 14 percent two decades ago, the report found.

"The growth in cohabitation as a context for first birth has roughly paralleled the decline in marriage," the report said.

The Daily Signal said the Census findings are pointing to new trends for the future.

"Marriage, not money, now marks the chief dividing line between classes in America," Lawrence Mead of New York University told the Daily Signal.